Understanding ECG
Learn how electrocardiograms work and what your results mean.

What is an ECG?

An ECG, or electrocardiogram, is a recording of the electrical activity of your heart. It is one of the most common tools used to assess heart health.

With each heartbeat, an electrical wave travels through your heart. This wave causes your heart to contract and pump blood.

A standard clinical ECG records 12 leads (or views) of the heart. Withings ECG devices sense the electrical activity of the heart through the left and right arm. This configuration is known as Lead I.

Diagram showing 12-lead ECG configuration versus single Lead I used by Withings devices

What practitioners look for on an ECG

A normal heartbeat on the ECG graph shows the time the electrical wave takes to move through your heart. There are three distinct patterns:

  1. The P wave

    The first wave on the graph, representing electricity moving into the upper chambers (atria) of your heart.

    ECG signal highlighting the P wave
  2. The QRS complex

    The second pattern, showing electricity moving through the lower chambers (ventricles).

    ECG signal highlighting the QRS complex
  3. The T wave

    The final wave, representing the electrical recovery of the ventricles as they return to a resting state.

    ECG signal highlighting the T wave

By measuring time intervals on an ECG, practitioners can determine if the electrical activity of your heart is too slow, too fast, or irregular.

What Withings ECG can identify

Clinical ECGs can reveal a range of heart conditions. Withings ECG devices focus on classifying your heart rhythm as normal sinus rhythm, atrial fibrillation (AFib), or inconclusive. This classification is meant to supplement — not replace — a professional medical evaluation.

Results you may see

Normal sinus rhythm
Your heart is beating in a regular, uniform pattern.
Example of a normal sinus rhythm ECG tracing
Atrial fibrillation
The upper chambers of the heart are beating chaotically instead of regularly. The P wave disappears and is replaced by a fluctuating baseline. The QRS complexes occur at irregularly irregular intervals.
Example of an atrial fibrillation ECG tracing
Inconclusive
The recording could not be classified. This can happen for several reasons:

Heart rate too low: A heart rate below 50 bpm during the recording prevents full analysis.

Heart rate too high: A heart rate above 100 bpm during the recording prevents full analysis.

Signs of other arrhythmia: The signal may indicate an arrhythmia other than atrial fibrillation, or a bundle branch block.

Example of an inconclusive ECG tracing
Noise
If there is too much interference, the recording cannot be classified. To improve signal quality: place your arm on a table or thigh, relax, stay still, and do not talk during the recording.
Example of an inconclusive ECG tracing

What to do with your results

  • Track regularly: Take ECG recordings periodically to build a history your doctor can review over time.

  • Share with your doctor: Use the Withings PDF Health Report to share your ECG recordings with a healthcare professional.

  • If AFib is identified: Contact your doctor to discuss next steps. Atrial fibrillation can often be managed effectively when identified early.

  • In an emergency: If you experience chest pain, difficulty breathing, or fainting, call emergency services immediately. Do not rely on a wrist-based ECG device in an emergency.

How to take an ECG with ScanWatch How to take an ECG with Move ECG
American Heart Association — What is Atrial Fibrillation?
ESC Guidelines for the Management of Atrial Fibrillation (2024)
StatPearls — Electrocardiogram (ECG)
Withings ECG devices are not intended to replace professional medical evaluation. The rhythm classification is meant to supplement — not replace — traditional methods of diagnosis. If you believe you are experiencing a medical emergency, call emergency services immediately.